1. Field of the Invention
The present invention relates to a deformed fiber which is a fiber spun from thermoplastic resin and is characterized in its specific shape where the filaments arranged in parallel are basic elements. More particularly, it relates to a deformed fiber which improves the applying and reinforcing properties of molded cement product by compounding with a hydraulic substance such as concrete and mortar as materials for public works and buildings whereby fiber for reinforcement of cement improving tensile strength, bending strength, shock resistance, cracking resistance, etc. can be prepared.
2. Prior Art
Synthetic fiber having modified cross section and uneven surface has been used in many fields for each of their purposes.
For example, pile yarn having modified cross section has been developed for artificial grass. However, monofilament and flat yarn having smooth surface have significant difference from natural grass due to their poor recovery from pressing bend and strong surface gloss and have disadvantages that they are not suitable as artificial grass. Pile yarn having modified cross section has been developed for solving such a disadvantage.
In various basic material sheets consisting of laminated sheet of textile and film, they are woven from a drawn yarn of modified shape having groove-like uneven surface so that laminated resin is invaded into spaces of the groove-like uneven surface to give a strong thermal fusion.
Besides the above, adhesive sheets where multifilament with many surface undulations and split yarn with naps are used as basic material whereby adhesion is improved and tufted products where lined latex is used together for strong unification have been available. As such, there have been many attempts in which modified cross section or surface undulation of synthetic fiber are utilized.
In addition, when deformed fiber which is cut in a short size is accumulated followed by bonding to give felt or nonwoven fabric, both flexibility and thermal fusion are improved and suppression of detachment of fiber can be expected and, therefore, deformed fiber is used as short fiber. Among various uses of deformed short fiber, the use as a fiber for reinforcement of cement by compounding with hydraulic substance such as concrete and mortar has been receiving public attention. Its background will be explained as hereunder.
Molded cement products using conventional concrete or mortar and cement constructions such as outer wall of buildings, inner wall of tunnels, inclined surface, etc. are relatively fragile as molded products. Especially, their physical properties such as tensile strength, bending resistance, bending toughness, etc. are insufficient and there are risks that the molded product shows cracks and is broken or that leakage of water or exfoliation takes place whereby many problems in terms of safety control have been pointed out.
In order to solve such problems, many molded cement products are reinforced by iron rods. However, there is a problem that transportation and assembling of iron rods increase cost for materials and for labor. Therefore, reinforcing means where less expensive fiber materials such as steel fiber, glass fiber, aramid fiber, carbon fiber and synthetic fiber are compounded with concrete instead of iron rods have been conducted.
Steel fiber is strong, has a high Young's modulus and is easily compatible with cement. In addition, there has been a proposal (U.S. Pat. No. 5,451,471) where V-shaped notches and grooves are formed on the steel fiber or the fiber is deformed near both ends so as to improve the adhesion to cement. However, since specific gravity of steel fiber is as high as 7.8, transportation and mixing work of the material are difficult. Further, there is a possibility that workers have their feet pricked by the steel fiber scattered around there upon application causing an injury. There is another problem that generation of rust lowers the reinforcing effect or deteriorates the beautiful appearance.
Although glass fiber uses an alkali-resistant glass, there is still a problem in durability and there is a disadvantage that the fiber is apt to be broken upon kneading with cement. In addition, fibers are apt to be tangled each other and a special kneader is necessary so as to form no fiber ball. Disadvantage of aramid fiber and carbon fiber is that they are expensive.
Unlike the glass fiber, synthetic fiber represented by resin of a polyvinyl alcohol type and a polypropylene type is less expensive, light in weight and strong and has a good handling property. However, it has a poor compatibility with cement and there is a problem that severe spots are apt to be generated on the molded cement product. In addition, short fiber in a simple shape has a disadvantage that it is apt to be dropped out from the molded cement product by bending stress and its reinforcing effect is not sufficient.
Therefore, many methods have been proposed where the short fiber shape of synthetic fiber for reinforcement of cement is improved to reduce the dropping out from molded cement product achieving a sufficient reinforcing effect. For example, short fiber consisting of elongated polyolefin tape where undulation is formed on the surface by an embossing treatment (Japanese Patent Laid-Open No. 116297/1999), short fiber prepared by elongation together with giving undulation thereto upon spinning, short fiber where nearly spiral projections are formed on the fiber surface and short fiber consisting of cleaved fiber of polypropylene film are available.
However, any of the above-mentioned disclosed art is insufficient. For example, in the deformed fiber where surface and cross section of the fiber are irregularly changed, it is difficult to keep a stable quality upon a continuous production. In addition, many disadvantages in the manufacture such as that productivity is poor because of difficulty in uniform spinning and winding, that conditions for production such as temperature setting upon extrusion and elongation are severe and that devices for the production are specific have been pointed out.
Further, modified polyolefin has been proposed for improving the adhesion of polyolefin short fiber to cement. For example, modification using a reactive silicon (Si(IV) moiety) is proposed in U.S. Pat. Nos. 4,710,540 and 4,952,631. However, it is inevitable that the chemical modification of polyolefin results in a high cost as compared with multipurpose polyolefin.